Method of electroless plating using a solution with at least two borane containing reducing agents

ABSTRACT

A solution for providing electroless deposition of a metal layer on a substrate is provided. A solvent is provided. A metal precursor is provided to the solvent. A first borane containing reducing agent is provided to the solvent. A second borane containing reducing agent is provided to the solvent, wherein the first borane containing reducing agent has a deposition rate of at least five times a deposition rate of the second borane containing reducing agent, and wherein the solution is free of nonborane reducing agents.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of and claims priority to pending U.S.application Ser. No. 14/297,352 filed on Jun. 5, 2014 and entitled“ELECTROLESS PLATING SOLUTION WITH AT LEAST TWO BORANE CONTAININGREDUCING AGENTS,” which is incorporated herein by reference in itsentirety for all purposes.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to a method of forming semiconductor devices on asemiconductor wafer. More specifically, the invention relates todepositing metal containing layers to form semiconductor devices.

In forming semiconductor devices, metal containing layers may bedeposited. Such a deposition may be provided by electroplating.

SUMMARY OF THE INVENTION

To achieve the foregoing and in accordance with the purpose of thepresent invention, a solution for providing electroless deposition of ametal layer on a substrate is provided. A solvent is provided. A metalprecursor is provided to the solvent. A first borane containing reducingagent is provided to the solvent. A second borane containing reducingagent is provided to the solvent, wherein the first borane containingreducing agent has a deposition rate of at least two times a depositionrate of the second borane containing reducing agent, and wherein thesolution is free of nonborane reducing agents.

In another manifestation of the invention, a solution for providingelectroless deposition of a metal layer on a substrate is provided. Asolvent is provided. A metal precursor is provided to the solvent.Borane dimethylamine is provided to the solvent. Morpholine borane isprovided to the solvent.

In another manifestation of the invention, a method for providingelectroless deposition of a metal layer on a substrate is provided. Thesubstrate is exposed to an electroless metal deposition, comprising ametal precursor, first borane containing reducing agent, and a secondborane containing reducing agent, wherein the first borane containingreducing agent has a deposition rate that is at least five times adeposition rate of the second borane containing reducing agent.

These and other features of the present invention will be described inmore details below in the detailed description of the invention and inconjunction with the following figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 is a graph of deposition rate in angstroms per second versuspercentage of DMAB.

FIG. 2 is a flow chart of an embodiment of the invention.

FIGS. 3A-B are schematic views of the formation of structures using theinventive process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference toa few preferred embodiments thereof as illustrated in the accompanyingdrawings. In the following description, numerous specific details areset forth in order to provide a thorough understanding of the presentinvention. It will be apparent, however, to one skilled in the art, thatthe present invention may be practiced without some or all of thesespecific details. In other instances, well known process steps and/orstructures have not been described in detail in order to notunnecessarily obscure the present invention.

Electroless metal/metal alloy plating solutions are generally made up ofone or more metal salts, a reducing agent, one or more complexingagents, one or more pH adjustors, a buffering agent, surfactant andadditives if needed. In most cases, one type of reducing agent in thebath is sufficient. If the primary reducing agent is not catalyticallyactive on the metal to be plated, the deposition cannot proceed. Toovercome this difficulty the substrate surface is activated usually byanother more catalytic metal or another reducing agent is added, inaddition to primary reducing agent, into the solution. This secondaryreducing agent initiates the deposition reaction on the substratesurface. After this step, the primary reducing agent can take over thedeposition reaction. Another possible purpose is to use two differentreducing agents to add additional alloying elements into the alloy to beplated. For instance, a CoWP deposition solution that containshypophosphite as the primary reducing agent will have usually less than1 atomic % boron in the film if a borane reducing agent is added to thedeposition solution.

Among the commonly used reducing agents boranes are a special categorybecause their reactivity is strongly influenced by the compound theyformed a complex with. Using two or more boranes present in the solutionas different complexes usually do not provide any of the above benefits.However, it has been unexpectedly found, such combination may be helpfulin adjusting the bath stability, initiation time, as well as depositionrate of the solution without changing the concentration of the othernon-borane solution components. In addition, the composition of thealloy using the combination of boranes closely matches the compositionof the deposit obtained with single borane source.

The deposition rate impact is strongest when there are only borane typesof reducing agents in the solution. For instance, in presence of largeamount of hypophosphite the deposition rate effect is significantlymuted. It was also found that the deposition rate can be convenientlyadjusted by the ratio and concentration of different boranes. FIG. 1illustrates the effect of borane mixtures (morpholine borane and DMAB)on deposition rate by providing a graph of deposition rate in angstromsper second versus percentage of DMAB.

Such an example of deposition rate adjustment using two borane reducingagents in a solution was found for the deposition of CoMoB alloy. Whenborane dimethylamine complex is used as reducing agent a deposition rateof 25 Angstrom/s is obtained. Changing the reducing agent to boranemorpholine complex the deposition rate reduced to 1.5 Angstrom/s. While25 Angstrom/s is too high to controllably deposit thin films (˜100Angstrom), 1.5 Angstrom/s is too slow. In addition, borane dimethylamineas the sole reducing agent causes the solution to become unstable. Ithas been unexpectedly found that a mixture of dimethylamine borane andmorpholine borane provides a stable solution, where the morpholineborane does not completely mask the deposition rate provided bydimethylamine borane. To achieve a deposition rate between these valuesa mixture of dimethylamine and morpholine complexes can be used.

The deposition rate reducing effect of morpholine borane works withother borane reducing agents as well. Such borane reducing agents can bediethylamine borane, tert-butylamine borane, ammonia borane, anddimethylsulfide borane.

In another embodiment, a solution may use two different borane reducingagents to simultaneously adjust multiple film properties. One reducingagent can shorten initiation time, but may cause high roughness. Theother reducing agent would reduce the roughness, but have a longerinitiation time. The combination of two provide a low roughness deposit(see Figure) and can meet the short initiation time requirement. In analternative embodiment, one reducing agent may provide fast initiation,but may cause nodule formation. Another reducing agent may have slowerinitiation, but may prevent or reduce nodule formation.

FIG. 2 is a high level flow chart of an embodiment of the invention. Inthis embodiment, an electroless deposition solution is provided,comprising a solvent, a metal precursor, dimethylamine borane (DMAB),and morpholine borane (step 204). A substrate is exposed to the solution(step 208).

In a preferred embodiment of the invention, an electroless depositionsolution comprising a solvent, a metal precursor, dimethylamine borane(DMAB), and morpholine borane is provided (step 204). This embodimentuses an aqueous solution.

A substrate is exposed to the electroless deposition solution. In thisexample, the substrate is a dielectric substrate with patterned metalsurfaces. FIG. 3A is a partial view of a substrate 300 with a pluralityof metal pattern surfaces 304 and dielectric surfaces 308. In thisembodiment, the metal pattern surfaces 304 are copper. In thisembodiment, the substrate is placed in a bath of the electrolessdeposition.

In this embodiment, the solution plates the metal pattern surfaces 304with a cobalt molybdenum boron (CoMoB) layer. In the bath, boranedimethylamine complex acts as a reducing agent providing CoMoBdeposition on the copper, since borane dimethylamine complex provides afaster deposition rate of 25 Å/s, which is needed to speed the initialdeposition on the copper surface 304. After a layer of CoMoB has beeninitially deposited on the copper surface 304, the borane morpholinecomplex deposition increases. FIG. 3B is a partial view of the substrate300 after a CoMoB layer 312 has been deposited.

This embodiment provides a fast deposition by using a faster boranecomplex, while providing deposition control, by providing a slowerborane complex. If a faster borane complex is used by itself, theresulting solution would be too unstable. Other reducing agents may maskthe faster borane complex, slowing the overall process. It has beenunexpectedly found that by adding a slower borane complex to the fasterborane complex, the overall process is not slowed, but the resultingsolution is made more stable. This embodiment also allows additionalcontrol of alloy additives in the resulting deposition.

In other embodiments, the metal precursor is at least one of a cobaltprecursor, a nickel, precursor, a copper precursor, or a molybdenumprecursor. In other embodiments, the solvent is water, dimethylsulfoxide (DMSO), ethylene glycol, or ionic liquids. Preferably, thesolution is hypophosphite free. Preferably, the solution furthercomprises at least one of a complexing agent, a surfactant, or a pHadjustment agent. In other embodiments, the pH and complexing agent maybe adjusted so that boron is not deposited the resulting deposited metallayer.

In other embodiments after a deposition is initiated using more than oneborane containing reducing agent, a single reducing agent may be usedfor further deposition. In other embodiments, three or four boranecontaining reducing agents may be used.

When borane dimethylamine complex is used as the reducing agent adeposition rate of 25 Angstrom/s is obtained. When borane morpholinecomplex is used as the reducing agent the deposition rate reduced to 1.5Angstrom/s. Therefore, in this embodiment the deposition rate of thefirst borane containing reducing agent, borane dimethylamine complex,with a deposition rate of 25 Angstrom/s, which is more than 16 timesgreater than the deposition rate of the second borane containingreducing agent, borane morpholine complex with a deposition rate of 1.5Angstrom/s. Preferably, the first borane containing reducing agent has adeposition rate at least five times the deposition rate of the secondborane containing reducing agent. More preferably, the first boranecontaining reducing agent has a deposition rate at least ten times thedeposition rate of the second borane containing reducing agent. Mostpreferably, the first borane containing reducing agent has a depositionrate at least fifteen times the deposition rate of the second boranecontaining reducing agent. Such solutions are free of nonboranecontaining reducing agents.

In another embodiment, two solutions, where each solution has adifferent borane reducing agent, are sequentially used. For example, amore active borane reducing agent may be applied in a first solution toquickly initiate deposition with no selectivity loss. Such a solutioncan be a non-recirculatable process, which might use and then discardthe solution. Next, a solution with a less active borane reducing agentmay be used to provide a more stable process. Such a solution may berecirculated. It is expected that the more reactive boranes will providefaster initiation time (the time needed to start the deposition reactionon a substrate) and lower bath stability (higher propensity forhomogeneous plating reaction). However, an unexpected outcome of thetests done with different borane shows that while tert-butylamine boraneprovide higher deposition rate than morpholine borane the latter oneinitiates faster consequently providing better selectivity. DMAB whichprovides higher deposition rate than morpholine borane can give higherbath stability.

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, and various substituteequivalents, which fall within the scope of this invention. It shouldalso be noted that there are many alternative ways of implementing themethods and apparatuses of the present invention. It is thereforeintended that the following appended claims be interpreted as includingall such alterations, permutations, and various substitute equivalentsas fall within the true spirit and scope of the present invention.

What is claimed is:
 1. A method for providing electroless deposition ofa metal layer on a substrate, comprising: exposing the substrate to anelectroless metal deposition solution, comprising a metal precursor,first borane containing reducing agent, and a second borane containingreducing agent, wherein the first borane containing reducing agent has adeposition rate that is at least five times a deposition rate of thesecond borane containing reducing agent, wherein the solution is free ofnonborane reducing agents.
 2. The method, as recited in claim 1, whereinthe metal precursor comprises at least one of a cobalt precursor, anickel precursor, a copper precursor, an iron precursor or a palladiumprecursor.
 3. The method, as recited in claim 2, wherein the firstborane containing reducing agent is at least one of tert-butylamineborane, ammonia borane, dimethylsulfide borane or dimethylamine borane(DMAB) and the second borane containing reducing agent is morpholineborane.
 4. The method, as recited in claim 1, wherein the first boranecontaining reducing agent comprises borane dimethylamine and the secondborane containing reducing agent comprises morpholine borane.
 5. Themethod, as recited in claim 1, wherein the first borane containingreducing agent is at least one of tert-butylamine borane, ammoniaborane, dimethylsulfide borane or dimethylamine borane (DMAB) and thesecond borane containing reducing agent is morpholine borane.
 6. Amethod for providing electroless deposition of a metal layer on asubstrate, comprising: exposing the substrate to an electroless metaldeposition solution, comprising a metal precursor, first boranecontaining reducing agent, and a second borane containing reducingagent, wherein the first borane containing reducing agent has adeposition rate that is at least five times a deposition rate of thesecond borane containing reducing agent, wherein the exposing thesubstrate to an electroless metal deposition solution, comprising:exposing the substrate to a first electroless metal deposition solution,comprising the metal precursor and the first borane containing reducingagent, wherein the solution is free of nonborane reducing agents; andsubsequently exposing the substrate to a second electroless metaldeposition solution, comprising the metal precursor and the secondborane containing reducing agent, wherein the solution is free ofnonborane reducing agents.